Studentská vědecká konference

Fermentation is a unit operation based on mass transfer from a gas phase to a liquid one. So, one key parameter required to study of this process is the volumetric mass transport coefficient. It is possible to calculate it with empirical correlation, based on geometrical and physical characteristics of the system considered. In order to create this kind of correlations, several measurements are required: a pilot-plant vessel was used for this purpose. Data for two and three impellers in different type combination, also with different diameters on the common shaft, was taken in order to guarantee a large validity range of the results. Usually, k_La correlations are based on gassed power input and superficial gas velocity. We tested several correlation types, evaluated their empirical parameters and proposed the correlation shapes suitable for fermenter design, operating and scale-up. The difference between the measured kla and the predicted one with a correlation is expressed through the standard deviation. In particular this correlation show the lowest standard deviation: kLa = 0,0055*(P/V)^0,7073*vs^0,4748  (1) SD = 28,9 %                                                   The Figure 1 below shows the difference between the measured values and the predicted one:   Figure 1: Comparison of measured and predicted k_La for correlation 1.

In recent years, there has been increasing demand for using nanoparticles in biomedical studies. These applications can only be successful with a high degree of control over the process parameters. Nucleation phase and growth of nanoparticles, desired size distribution of particles and their morphology are main objectives of a synthesis process. For further use of nanocarriers towards targeted cells or tissue, the  surface modification of nanoparticles is the next step. The aim of this work is the production of uniform silica nanoparticles by the continuous microfluidic system. Silica nanoparticles are produced based on Stöber process in a microchip prepared from PDMS (Polydimethylsiloxane) by a standard soft lithography method. The dispersed phase of the system forms ethanol with reagents (ammonia and TEOS) and the continuous phase is fluorinated oil FC-40. The surface of all microfluidic channels is modified with a silanizing agent (1H,1H,2H,2H-perfluorodecylsilane). Final particle size and morphology are analysed using SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope) and DLS (Dynamic Light Scattering) are used.

The objective of this research is to assess the pH dynamic behaviour of Urea-Urease system in a membrane reactor by varying pH of stock solutions, flow rate and concentrations of urea and urease solutions. The urease performs enzyme-catalyzed hydrolysis of urea under acidic conditions to yield ammonia and CO2. The membrane reactor consists of the main reactor, where the urease with specific pH is fed and the flow-through reservoir, where urea with specific pH is fed. Both the reactor and reservoir were coupled via dialysis membrane Spectra/Por 7 MWCO:1000, both the reactor and reservoir were stirred at 1050 rpm, the pH was monitored using a pH electrode immersed in the reactor part. The system was closed to the atmosphere. According to work of Bánsági, Jr. et al., (2014),  J. Phys. Chem. B 118, 6092-6097, pH oscillations can occur in a membrane system loaded with urease when ratio of permeances of H+ ions and urea is between 3.3 and 20 towards the H+ ions. Our measurement shows the membrane have unequal permeances for both H+ and urea, the ratio is 2.7 towards the H+ ions. Parameter space has been mapped by marking multiple stationary states and oscillatory regions. pH oscillatory behavior has been found with the difference between minima and maxima ~1.2 pH units.

Interfacial properties can be often difficult to measure. An alternative approach is to derive all missing information about interfaces from thermodynamics in a self-consistent manner. Density functional theory (DFT) is a powerful tool enabling to calculate thermodynamic properties. The theory works with energy functionals of density functions distributed along spatial coordinate(s). Subsequent minimization of this functionals lead to finding the density profiles which are starting points towards physical properties of systems such as surface tension, etc. In this work we simplified the description of one-component system with (l)-(g) interface as a spatially one-dimensional problem employing Van der Waals equation. DFT was applied to the mentioned system in order to find density profiles. Further steps involved numerical solution of boundary value problem for the nonlinear second order differential equation. As this work is a familiarization with the DFT theory the next step will be a closer approach to real systems and thus a three-dimensional model with a more accurate description of state behaviour of two-component systems to find desired interface properties and thus to participate in a building of the self-consistent model for foaming and other applications.

In this work, porous microparticles, so called microclusters, were prepared by aggregation of polymeric primary particles under completely destabilized conditions. The polymeric nanoparticles have core-shell structure, where the core is formed by highly crosslinked polymethyl methacrylate and the shell is formed by mixture of polymethyl methacrylate and polybutylacrylate, resulting in different mechanical properties of core and shell. The soft character of the shell increases the adhesion of the nanoparticles, resulting in variable mechanical strength of formed microcluster. Main goal of this work was to investigate impact of operating conditions on the mechanical properties of these microclusters. Parameters included in the work are temperature, stirring speed and shell thickness. Analysis of the microcluster properties was done by static light scattering. Creating of microclusters by physical locking method over the chemical polymerization method has several advantages like reduction of aggregation time, reduction of the need to use chemicals and higher flexibility of the process.

3D printing is nowadays fast-growing sector with high perspective in pharmaceutical industry. Large number of pharmaceutical companies is trying to enlarge their traditional ways of producing drugs with techniques based on 3D printing, especially FDM 3D printing (Fused deposition modeling). First achievements were already reached and the first 3D printed drug called Spiritam is available in the USA.  The goal of this work is to print tablets by commercial FDM printer that will contain two active pharmaceutical ingredients (APIs). Main advantage of such tablet is dissolution kinetic controlled by designed porosity and internal surface area of the tablet. The spatial concentration of the API in the tablet is also well defined according to required treatment. As a printing material, the FDM 3D printers use filaments that are produced by hot-melt extrusion technique. Mixture of carrier polymers, API and plasticizers were melted together in nozzle of an extruder to produce homogenous filament. Filaments were analyzed and results were compared with fully printable referent filament (obtained from previous project). In the final step two filaments (containing different API) will be used to print a tablet according to model designed in AutoCAD software.  

Sustained release injectable suspensions (also called “nanoparticle depot systems“) are relatively new phenomenon in clinical practice. Compare to the conventional treatment methods, these dosage forms provide a number of benefits such as: lower frequency of administration, blood level remains within therapeutic range, etc. These suspensions may be administered in the form of a poorly soluble drug and the release time of the Active Pharmaceutical Ingredient (API) of such medication is dependent on the particle size and the specific surface area of drug particles. The conversion from the insoluble drug to the soluble API occurs through natural mechanisms of the human body (enzymatic hydrolysis). In drug development, it is very important to have reliable method how to evaluate drug dissolution profile in in vitro conditions before clinical trials on animals and humans. For this purpose we have developed a dissolution method that can provide the data of dissolution kinetics. Within this method a parametric study on the laboratory mill was carried out that allows us to prepare suspnesions of defined particle size distribution, two analytical methods (HPLC an LC-MS) to determine concentration of API and prodrug were created and a sample preparation procedure was designed.

Graphene has received considerable attention in recent years due to its remarkable thermal, electrical and mechanical properties. Its large surface-to volume ratio makes it a promising option as a filler for polymers. But synthesis of true monolayer graphene provides considerable challenges and can also be extremely costly, therefore an oxidised derivative of graphene - graphene oxide, has attracted attention due to its relative ease of preparation. The functionalities (like hydroxyl, carboxyl, carbonyl and epoxy) also support the uniform distribution of rGO nanosheets in a polymer matrix. Polyaniline is perhaps the most extensively studied conductive polymer due to its relatively simple synthesis, environmental stability, economic viability and its chemical, electrical and optical properties. Combining the excellent properties of graphene with the advantages of polyaniline aims to improve many of the properties of the resulting composite material which might find variable applications for example in supercapacitors, flexible sensors or materials for CO₂ capture.